Geology of the Northern Convoy Range, Victoria Land, Antarctica

Journal of Maps ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/tjom20 Geology of the northern Convoy Range, Victoria Land, Antarctica Giovanni Capponi , Chiara Montomoli , Stefano Casale & Matteo Simonetti To cite this article: Giovanni Capponi , Chiara Montomoli , Stefano Casale & Matteo Simonetti (2020) Geology of the northern Convoy Range, Victoria Land, Antarctica, Journal of Maps, 16:2, 702-709, DOI: 10.1080/17445647.2020.1822218 To link to this article: https://doi.org/10.1080/17445647.2020.1822218 © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group View supplementary material Published online: 08 Oct 2020. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=tjom20 JOURNAL OF MAPS 2020, VOL. 16, NO. 2, 702–709 https://doi.org/10.1080/17445647.2020.1822218 Science Geology of the northern Convoy Range, Victoria Land, Antarctica Giovanni Capponi a, Chiara Montomoli b, Stefano Casalec and Matteo Simonettib aDISTAV, University of Genoa, Genoa, Italy; bDipartimento di Scienze della Terra, University of Turin, Turin, Italy; cDipartimento di Scienze della Terra, University of Pisa, Pisa, Italy ABSTRACT ARTICLE HISTORY In this paper, we supply a geological map of the area between 76°–76°30′S and 159°–163°E, that Received 14 November 2019 was the only missing portion to complete an entire coverage of Victoria Land, filling the gap Revised 17 March 2020 between the GIGAMAP program (to the north) and the maps by the New Zealand Antarctic Accepted 7 September 2020 program (to the south). The mapped area encompasses an early Paleozoic basement, and a fl KEYWORDS at-lying cover of sedimentary and igneous rocks, Permo-Triassic to Jurassic in age. The Geological mapping; Convoy basement consists of large bodies of the Granite Harbour Igneous Complex, a granitic Range; Victoria Land; complex linked to the Ross Orogeny. After the early Paleozoic Ross Orogeny, the area was Antarctica uplifted and eroded, and the sandstones of the Beacon Supergroup were deposited on the resulting erosion surface. The Beacon Supergroup sandstones were in turn covered and in most cases incorporated into the volcanic and sub-volcanic rocks of the Jurassic Ferrar Group. 1. Introduction Field activity was organized in daily missions from the Italian Mario Zucchelli Station (2017/2018) and In northern Victoria Land (Antarctica), the activity of in a period of stay in a tent camp (2018/2019), at German and Italian geologists has resulted in several Starr Nunatak (75°54′S162°35′E), in order to be able geological maps (Carmignani et al., 1987; Ganovex & to reach the most distant sectors of the study area. Map- ItaliAntartide, 1991; Ganovex & ItaliAntartide, 2003; ping was coupled with the collection of rock samples Ganovex Team, 1987). Additionally, in 1995, German that we studied in thin section after the expeditions, and Italian geologists signed an agreement of in order to better characterize the lithotypes. cooperation (the GIGAMAP program, Capponi The topographic base comes from a mosaic of two et al., 2002) to cover the entire northern Victoria 1:250,000 USGS quadrangles i.e. the Convoy Range Land region with new geological mapping at the and the Franklin Island quadrangles; they were used scale 1:250,000. In the Dry Valleys area, geological both in the field and for the final construction of the mapping has been carried out principally by New Main Map. The Franklin Island quadrangle includes Zealand geologists (Cox et al., 2012; Gunn & Warren, a large area of the Ross sea, with two small islands in 1962; Pocknall et al., 1994), and their maps, together the eastern part, i.e. the Beaufort and Franklin islands, with the GIGAMAP maps, give an almost complete that we were not able to visit and map. Because of this, coverage of Victoria Land. However, the area between ′ we excluded from the Franklin Island quadrangle the 76° and 76°30 S (the northern part of the Convoy area covering the sea and the unvisited islands and Range and Franklin Island quadrangles, 1:250,000 join the trimmed area with the Convoy Range topographic sheets by USGS) has yet to be mapped quadrangle. in any detail and is devoid of updated geological observations: the aim of this paper is to supply the geological map of this area. 3. Geological framework The Convoy Range-Franklin Island quadrangles encompass an early Paleozoic granitic basement, and 2. Methods a flat-lying cover of sedimentary and igneous rocks, The 1:250,000 scale Main Map covers an area of about spanning in age from Permo-Triassic to Jurassic. 6665 km2. Mapping was performed during two Ita- The early Paleozoic basement consists of large liAntartide expeditions (XXXIII Expedition in austral bodies of the late Cambrian-early Ordovician Granite summer 2017/2018 and XXXIV Expedition in austral Harbour Igneous Complex, enclosing minor bodies of summer 2018/2019). Field work was carried out by a metamorphic rocks of the Wilson Terrane. The three-person team and was helicopter-supported. Wilson Terrane includes low-medium- to high-grade CONTACT Giovanni Capponi [email protected] DISTAV, University of Genoa, Corso Europa 32, 16132 Genoa, Italy © 2020 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrest- ricted use, distribution, and reproduction in any medium, provided the original work is properly cited. JOURNAL OF MAPS 703 metamorphic rocks of inferred Precambrian-Cambrian coast of the Ross Sea, and are characterized by the age, deformed and metamorphosed in the early Paleozoic association of the syn-tectonic Larsen granodiorite Ross Orogeny (late Cambrian–early Ordovician). After with post-tectonic granite. Such rocks represent a typi- the Ross Orogeny, the area was uplifted and eroded, cal arc-related calc-alkaline orogenic suite, linked to and the sandstones of the Beacon Supergroup were the subduction zone magmatism associated to Ross deposited on the resulting peneplain surface. The Beacon Orogeny. The dominant rock type is an unfoliated to sandstones were in turn intruded by the sills of the Jurassic weakly foliated metaluminous biotite granite and Ferrar Dolerite, and in most cases incorporated into the granodiorite. Radiometric age data (U–Pb on zircon) dolerite. indicate that the emplacement sequence of the Granite Harbour Igneous Complex spanned nearly 30 Myr, from 521 to 481 Ma (Bomparola et al., 2007; Giaco- 4. Wilson Terrane mini et al., 2007); no data specifically related to this 4.1. Wilson metamorphic complex (Wa) quadrangle are available. At many places, the dominant granitoid type is In this area, the Wilson Metamorphic Complex intruded by the younger Irizar Granite (GHgra), that includes low-to medium-grade metasediments; such is a homogeneous, unfoliated, equigranular, medium- rocks are restricted to small bodies and slivers, occur- to coarse-grained syeno-monzogranite, characterized ring at Mt Murray, south of Mt Chetwynd and at by pink–red colour, due to the presence of pink alkali northern Walker Rocks. The protoliths of these meta- feldspar. A 489 ± 4.4 Ma U–Pb zircon crystallization sediments appear to belong to a unique sequence of age was obtained at Cape Irizar (Rocchi et al., 2009), fi ne- to medium-grained siliciclastic sediments, with in agreement with Di Vincenzo et al. (2003),whosup- intercalations of conglomerate (Walker Rocks, Figure plied an age of 486.1 ± 8.4 Ma by Ar–Ar and Rb–Sr 1(A)). Their depositional age is widely unknown and a techniques. Major Irizar outcrops are in the northern late Neoproterozoic to Cambrian age is likely, on the cliffs of Mt Gauss and in the western slopes of Mt Ende- basis of detrital white mica geochronology (Di Vin- vour; Irizar granite occurs also as m-thick dykes, with cenzo et al., 2014; Tessensohn & Henjes-Kunst, the same age of emplacement (Rocchi et al., 2009). 2005). Such metasediments underwent metamorphic equilibration from low to high grades, during the 4.3.2. Diorite and gabbro (GHt) Ross Orogeny (Carmignani et al., 1987; Casnedi & Large bodies of unfoliated to weakly foliated micro- Pertusati, 1989; Castelli et al., 1997; Lombardo et al., gabbro-microdiorite occur in the area of Mt Smith, 1987; Skinner, 1989). beneath the light grey granite. Due to the dark colour, they resemble Ferrar dolerite, but the clear gradational 4.2. Johnnie Walker formation (Wf) contact with respect to the overlying granites (Figure 1 (B)) rules out this option and supports a genetic This formation crops out at the southern area of relation with the Granite Harbour Igneous Complex. Walker Rocks, in the centre of the study area, and con- Other rocks related to the Granite Harbour Igneous sists of unmetamorphosed andesite, brecciated ande- Complex are the Vegetation Lamprophyres, that con- site, rhyolite and granophyric rhyolite (Tessensohn stitute a widespread association of hypabyssal tabular et al., 1990). The rock types and the field observations intrusions (Rocchi et al., 2009), with hundreds of sub- suggest a formation in a sub-volcanic environment. vertical mafic dikes, with thicknesses around 1 m, and Such rocks unconformably overlie the meta- an overall strike between NE–SW and NNE–SSW. morphic rocks of the Wilson Terrane and are intruded Dykes sampled at Bruce Point, Cape Hickey and Mt by the Granite Harbour Intrusives. The age of these Endevour returned an Ar–Ar age around 490 Ma rocks is unknown, but must be older than the empla- (see Rocchi et al., 2009, for details). cement of the ∼490 Ma Granite Harbour Igneous Complex. The temporal position of these rocks, between Ross-age metamorphic rocks and the post- 5.

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